Obstructive sleep apnea (OSA) is a common disorder which produces considerable morbidity and mortality. The disorder arises during sleep when the victim undergoes repeated cessation of breathing. This cessation results from an obstruction of the throat air passage (pharynx) due to severe narrowing or a collapse of the throat air passage. Repeated cessation of breathing reduces blood oxygen and disturbs sleep. Reduction in blood oxygen can cause hypertension, heart attacks and strokes. Additionally, sleep disturbances can produce excessive daytime sleepiness, headache, depression, irritability and cognitive impairments.
Medical research over the past decade has produced a standard approach to obstructive sleep apnea therapy, known as nasal continuous positive airway pressure (CPAP). In this therapeutic approach, a patient's nose is covered with a mask that forms a pressure seal with the surrounding face. While the patient sleeps, the mask is pressurized to a level that distends the collapsible throat air passage, thereby preventing obstruction.
This therapeutic approach provides two significant advantages: it is uniformly effective and it is entirely benign. A major disadvantage of this approach is that the patient must remain overnight in a hospital sleep center to undergo a full night polysomnography study with the pressure mask in place to determine the therapeutic level of pressure. A further disadvantage of this approach is that the pressure delivered to the patient during the polysomnography study is constant and fixed at the prescribed level, even though the patient's requirements may vary throughout the night and from night-to-night.
The overnight study presents a potential bottleneck to treating a high volume of patients with obstructive sleep apnea because it typically requires two full night polysomnographic studies for each new patient: one to establish the diagnosis (diagnostic-polysomnogram) and another to establish the aforementioned therapeutically optimal pressure (therapeutic-polysomnogram). The therapeutic polysomnographic study is necessary to determine the minimum level of pressure required to produce a patent pharyngeal airway (i.e., to determine the necessary therapeutic pressure required for properly treating the patient). These studies, performed in a specialized hospital sleep center, allow a specialist to specify the pressure to be used when prescribing nasal CPAP therapy. For this reason, the therapy cannot be prescribed by an internist or general practitioner.
Due to the requirement of two night polysomnographic studies, hospital sleep centers are crowded even though only a small percentage of obstructive sleep apnea victims are presently being treated. Further, the significant cost of the overnight polysomnographic study by a hospital sleep center represents a significant obstacle to diagnosing and treating the large population of sleep apneics. The backlog of undiagnosed and untreated obstructive sleep apnea patients thus represents a substantial public health problem.
To address the foregoing drawbacks of existing approaches to diagnosis and treatment of obstructive sleep apnea, recent commercial technology provides overnight, unattended monitoring of breathing in the patient's home. Such unattended monitoring generally permits the physician to diagnose obstructive sleep apnea without requiring a diagnostic overnight study in the hospital sleep center. However, a hospital sleep center is still required for establishing the therapeutically optimal pressure of nasal CPAP in each patient. Accordingly, medical practitioners have been slow to use the new monitoring technology for diagnostic purposes since the patient must, in any case, be referred to a sleep center for a full night therapeutic polysomnographic study.
While there is a continuing need for CPAP technologies, clinical studies and general clinical experience indicate that nasal CPAP is not always an effective treatment for many patients with obstructive sleep apnea, particularly those with symptoms of mild to moderate severity.
Various surgical approaches have been employed to correct the structural abnormality of the pharyngeal airway. Excluding massive reconstruction of the mandibular, maxilla and/or tongue, the only widely employed surgery has been uvulopalatopharyngoplasty (UPPP). However, results with UPPP are disappointing unless patients are selected by pharyngeal endoscopy during sleep and, even then, the long term benefits are questionable. Laser-assisted uvulopalatoplasty (LAUP) is a new approach which has been recommended for obstructive sleep apnea. No studies have reported the effectiveness of LAUP in the treatment of obstructive sleep apnea, but there is little reason to anticipate that it will be more effective than UPPP although it may be more convenient, less expensive and may prove to be a useful adjunct therapy to be used in combination with mandibular positioner (MP) therapy for patients in which MP therapy does not eliminate apneas and hypopneas.
Stationary oral appliances which draw the tongue forward have been used in the treatment of snoring. In addition, some recent studies suggest that a fixed oral appliance (i.e., mandibular positioner) which holds the lower jaw (i.e., mandible) of the patient forward as the patient sleeps is effective in treating obstructive sleep apnea, especially mild obstructive sleep apnea. Studies have shown that ventral displacement of the mandible enlarges the pharyngeal airway and acts to prevent its closure. Conventional mandibular positioners are constructed by a dentist or orthodontist at a fixed position for holding the mandible forward. The proper fixed position is determined through trial and error by having the patient try a series of mandibular positioning devices until the most effective one is found. Once the mandible displacement is set for the device, it remains stationary with no accommodation for variations in the obstructive sleep apnea, such as body position, sleep state, effects of drugs, and congestion of the patient.
An adjustable mandibular positioner, developed by Dr. A. Lowe, Head, Department of Orthodontics, University of British Columbia allows incremental adjustment of the ventral displacement of the mandible. This device is referred to as a screw adjustable mandibular positioner (SAMP), because its upper and lower full arch orthotics are connected by a manual screw device which is adjusted by the patient or dentist to set the magnitude of mandibular advancement. Thus, the patient or dentist can progressively advance the mandible with the SAMP over a period of weeks to months so that mandibular muscles and ligaments can adjust, thereby allowing greater ventral displacement and minimizing side effects.
Accordingly, it would be desirable to render the therapy of obstructive sleep apnea more practical and convenient. To achieve this end, a method and system for automatically establishing the desired mandible advancement for a patient during changing sleep conditions is needed. More particularly, a system is needed with an adaptively controlled mandibular positioner that automatically adjusts to a patient's needs throughout the night and from night to night.